Fan blower



Patented .lune 10, i924.

f STATES PAT-ENT ALFRED E. SELIG, F NEW YORK, N, Y.

FAN BLOWER. n

Application led June 19, 1920.l Serial No. 390,084..y

T0 all whom t may concern Be it 'known that I, ALFRED E. Sannio., a citizen of the United States, residing at New York city, in the county of New York, State of New York, have invented certain new and useful Improvements in Fan Blowers;

and I do hereby declare the following to bea "full, clear, and exact description ofthe invention, such as will enable others skilled in the artto which itappertains to make and use the same.

The present invention relates to fan blowers of the kind employed for ventilation,

forced drafts for furnaces, etc.

1 Fan blowers of this type usually embody a fan of the propeller blade type mounted for rotation in a casing or duct, through of discharge.

which the air is forced to the desired point Such fans have usually been made with the casings of cylindrical bore and closely fitting the periphery of the fan blades.

In fans of this character there are certain losses of pressure and capacity sometimes at; tended with the production of eddy currents anda tendency for the air to blow back to* ward the suction side of the fan, and different methods have been proposed to overi come the difficulty.

` The most successful methodl heretofore employed of which I am aware consists in enlarging the casing of the fan around the periphery of the fan blades on the delivery side to about half the depth or axial dimension of the fan, and' curving the face of the casing'where its small diameter kmerges intothe larger diameter to provide a deflecting surface for directing the radially discharged air into an axial path'of movement alongA with the air discharged from nearer the middle of the fan. This construction lessens the choking effect and back-blowing of the 'f straight casing fan, but is open to the objection that the air which escapes radially from the periphery of the fan blades into the enlarged portion of the casing has not as high 'jaxial `velocity as the air which leaves the blades from their radial edges, with the result that the ultimate or average velocity of the entire moving air column is reduced by Y theslower moving currents discharged from rthe periphery of the blades and deflected byy *the casing.

By the invention of this application I more eifectually relieveV the choking effect and blowing back and at the same time avoid the inherent defects' of the blowers ofthe prior art.

My improved fan also provides a greater blade area for the same diameter'ofcasing. This feature is of particular importanceas the space available for the duct or casing frequently limitsthe size of thefan where greater capacity would be desirable.` y

YVith rthe .above objects in view my invention consists in the construction shown in the accompanying drawing, wherein-'- 1 Figure l is a diagrammatic view showing a preferred curve for the fan casing incomparison with a true parabola;

Fig. 2 is a vertical sectional view of a fan embodying my invention;

Fig. 3 is a front view of the fanlooking I The fan 1 is mounted kin, a casing 3 through l which air is to be directed to the furnace fire box or other place of delivery. The portion 4l of the casing which encloses `the fan is curved instead of cylindrical, the curvepreferably conforming to the parabolicdeiiv'ative hereinafter described.y The endsY of. the

vfan blades are not cut oif at theirk endsat right angles to the radius of theffa'n, but

are curved to'conform to the curvature lof the casing. so as tov allow more clearance bctween the blades and theinner surface of the casing. Beyond thedelivery or front edge of the fan the casing is gradually curved into the cylindrical portion 5 which forms y the duct for the delivery of the airand which may be itself inserted in thefurnace wall or connected to a longer air line ifthe' air is to be used at a distance from'the blower.,

I have found that the air in its passage,t

through the fan is acted upon byforces tending to drive the air in three different directions. In the first place ,the air is forced axially away from the fan by thetinclined faces of the fan blades. Thisaxial' movenient is not in lines strictly parallel with the axis of the fan but, due to the pitch and rotation of the blades, there is a rotaryvor circumferential component lwhich with the axial component gives tothe air a ytendency the manner indicated in F ig. l.

to rotate inthe casing as well as advance longitudinally, .the tendency to rotate being gradually diminished by the friction of the stationary casing walls as the air advances toward the delivery end of the casing.

In addition to these two components the air has a radial component, due to the centrifugal force of the air from its rotation with the fan. In a fan of ordinary construction with a closely fitting cylindrical casing this tendency to radial movement sets up eddy currents in the volume of air, sometimes causing a blowing back of the airtow'ardthe suction side of the fan, due to the fact: that the air impinging against the casing is thrown back by the casing into the path of the fan blades, and across the streams of Aair ldischarged directly from the fan blades. t f

To relieve the choking effect as completely as possible, the curve of the flaring portion of the casing is preferably determined in As here shown the curve A is a parabola Vwith its focus at F, the proportions and dimensions of the parabola being` determined from the resultant of the radial and axial components of the air current, which components vary chiefly with the speed of rotation, the diameter of the fan, and the pressure, but are also affected by the pitch. After the curve A is determined for the particular installation-of fan a projection of the. curve is made, the angle of projection being propoi tioned to the circumferential component of the air current which varies chiefly with the pitch of the fan. For the fan shown in the drawing the angle of projection is 30 degrees. In deriving the e30-degree projection .from the curve A as plotted on the drawing board, the curve will be rotated on theperpendicular to its axis at the vertex through: an angle of 3() degrees, and then projected back to the plane of the paper, forming the curve B, the effect being to foreshorten the parabolal just as the air currents are foreshortened by a circumferential 'component of corresponding degree. Hence, a surface generated by the rotation of the projected parabola about its axis will pro- .duce a deflecting surface which will reflect air currents fromthe direction of the focus of the parabola. which impinge against it in a generally `axial direction.

The air discharged from the front of the fan does not leave the fan in the same direction with regard to its axis of Vrotation inall parts of the fan, The air discharged near the periphery of the blades has a greater centrifugal moment than the air discharged from points on the blades nearer the axis. Hence it may be said that the column of air leaving the fan, if uninfluenced by a casing of any description, would be of la flaring or conical configuration, that is,

'axis of rotation.

the air currents making up the column may` be considered as having a direction proceeding generally from a common point on the If this point. is taken as the focus of the parabola A in designing the casing, the greater portion of the air column will be uniformly reflected by the casing into substantially parallel paths, and the tendency to the formation of eddy, currents, the choking effect and the blowing back, will be materially reduced.

Instead of placing the focus at the ape of the conical air current the focus may be displaced slightly from lthis point, sotthat the air currents, insead of being reflected parallel to the axis of rotation, will still slightly diverge and `follow the wall offthe casing, being gradually brought into parallelism by the convergence of the parabola into the cylindrical casing.

Preferably the curve of the casing continues as shown in Fig. 2 beyond the delivery edge of the fan blades so as togradually check the tendency to radial movement in the air and deflect the air into an axial moving air column of substantially uniform velocity throughout. In case, however, space does not permit the use of a casing of this size in proportion to the sizeof fan necessary for its volume of air required, Imay construct the fan and casing as shown in Fig. 4. As here shown the curve of the expanded portion of the casing is so proportioned as to blend directly into .the cylindrical portion of the casing at the delivery edge of the blades. By properly curving the surface of the casing any air reflected from the face of the casing would be deflected axially out of the fan instead of back inthe path of the blades. With this type of fanit is advisable to have the parabola shaped to refiect the air currents slightlyk more .than

when the curve extends beyond the front of the fan to avoid too great a density at the casing wall.

It will be noted that with this type fof Afan the effective blade area is but little less than that of a straight casing fan with .thesame diameter of casing, while in a fan of the present expanded casing type, the same size casing would only accommodate a fan kof a diameter equal to the reduced intake open-y ing of the casing. .p ,f

It will of course ,be understood that the direction of the air currents varies withthe same fan under different operating conditions and that there is no definitely fixed point from which the air curre-ntsthroughout the whole area of the fan can be said to originate, but an approximate .point can be located for the focus of the parabola whereby the greater portion ofthe air column will be deflected. substantially in the manner described. .i

It is also to be understood that the invention is not limitedV to a parabolic curve or to the disclosed arrangement of the fan in the casing except in so far as defined in the appended claims.

I claim:

l. In a blower, the combination of a fan of the propeller type having the ends of its blades diverging from the intake to the delivery side of the fan on a curve proportioned to the diameter and intended speed of the fan, and a casing having a portion enclosing the fan blades, said casing having its surface at the periphery of the blades diverging in conformity with the divergence of the fan blades.

2. In abloWer the combination of a fan of the propeller type having the ends of its blades diverging from the intake to the delivery side of the fan on a curve proportioned to the diameter, pitch and intended speed of the fan, and a casing having a portion enclosing the fan blades, said casing having its surface at the periphery of the blades diverging in .conformity with the divergence of the fan blades.

3. In a blower the combination of a fan of the propeller type, and a casing therefor having its surface enclosing the periphery of the fan blades curved to approximately parabolic shape, the factors of the parabola being proportioned to the diameter and intended speed of operation of the fan.

4. In a blower the combination 'of a fan of the propeller type, and a casing therefor having its surface enclosing the periphery of the fan blades curved to approximately parabolic shape, the factors of the parabola being proportioned to the diameter and intended speed of operation of the fan, said fan having the ends of its blades curved to 40 conform to the curvature of the casing.

5. In a blower the combination of a fan of the propeller type, and a casing therefor having its surface enclosing the periphery of the fan blades curved to approximately parabolic shape, the factors of the parabola being proportioned to the diameter, pitch and intended speed of operation of the fan.

, 6. In a blower the combination of a fan of the propeller type, and a casing therefor having its surface enclosing the periphery of the fan blades curved to approximately parabolic shape, the factors of the parabola being proportioned to the diameter, pitch and intended speed of operation of the fan, said fan having the ends of its blades curved to conform to the curvature of thecasing.

7. In a blovver, the combination of a fan of the propeller type and a casing therefor having its surface enclosing the periphery of the fan blades curved to approximately parabolic shape, the deviation from a `true parabolic section being in proportion approximately to the pitch of the fan.

8. In a blovver the combination of a fan of the propeller type and a casing therefor having its surface enclosing the periphery of the fan blades curved to the shape derived from a parabola, the parabola being proportioned approximately to the diameter and intended speed of operation of the fan, and the curve of the casing being derived from the parabola by an angular projection of the parabola proportioned approximately to the pitch of the fan.

In testimony whereof I affix my signature.

ALFRED E. SEELIG. 

